1. Field of the Invention
The present invention relates to an apparatus and a method for measuring the curvature radii of spherical and cylindrical surfaces.
2. Description of Prior Art
Based on the principle of trigonometric functions, as shown in FIG. 1, the curvature radius of a spherical or cylindrical surface is given by: ##EQU1## wherein h is the sagittal depth;
D is the ball-ring-distance over which the measure is made; PA1 r is the radius of each of the ball rings. PA1 preparing an apparatus for measuring the curvature radii of spherical and cylindrical surfaces as metioned above; PA1 preparing a spherical lens or a cylindrical lens; PA1 putting the spherical lens or the cylindrical lens on the apparatus, with the lens supported by the four ball rings, to lower the probe to a distance h; and PA1 calculating the curvature radius of the spherical lens or the cylindrical lens according to the equation as follows: ##EQU2## wherein R is the curvature radius of the spherical lens or the cylindrical lens; PA1 h is the lowered distance of the probe; PA1 D is equal to .sqroot.2C for the spherical lens or is equal to C for the cylindrical lens; PA1 r is the radius of each of said ball rings.
A conventional contact-type measuring apparatus comprises three similar ball rings which are arranged into a equilateral triangle having a side length D. When a spherical lens is measured, it is put on the measuring apparatus and supported by the three identical ball rings. A probe is movably mounted at the center of the equilateral triangle for measuring the sagittal depth h. The radius r of the ball rings is known and thus the curvature radius R can be found according to the above equation (1). However, the conventional measuring apparatus can not be utilized to measure the curvature radius of a cylindrical surface because a cylindrical lens can not be stably supported by the three ball rings of the conventional measuring apparatus.